Acute Respiratory Distress Syndrome in Trauma Patients

Stephen Derdak;

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Excerpt

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common in patients with severe traumatic injuries and contribute to morbidity and mortality. ALI is defined as acute onset of pulmonary infiltrates (not due to congestive heart failure or fluid overload) with a Pao2/FiO2 ratio ≤300, whereas ARDS is defined as a Pao2/FiO2 ratio ≤200. Despite oxygenation severity criteria forming the basis for the ALI/ARDS definition, baseline oxygenation has not been predictive of mortality. In contrast, initial dead space fraction, oxygenation response to a brief PEEP trial, oxygenation index, etiology of ARDS, and the percentage of recruitable lung have correlated with mortality. Mortality is closely linked to the development of multi-organ failure, although approximately 10% of patients die with refractory hypoxemia. Trauma patients have unique causes of ALI/ARDS to include: lung contusion, blast injuries, fat embolism syndrome, transfusion-associated lung injury, traumatic pneumonectomy syndrome, neurogenic pulmonary edema, and smoke inhalation. Traumatic trachea-bronchial tears, abdominal and thoracic compartment syndromes, elevated intra-cranial pressure, and the frequent need for patient transport may further complicate mechanical ventilator management.Studies of mixed (medical and surgical) populations of ALI/ARDS patients have demonstrated improved mortality using conventional mechanical ventilation strategies that employ lower tidal volumes (≤6 mL/kg) based on patients’ predicted body weight (PBW), compared with higher tidal volumes. Recent data suggests that initial use of lower tidal volumes in patients at risk may reduce the development of ALI/ARDS. Despite the use of lung protective ventilation strategies, mortality can be >50% in patients with severe disease. A number of alternative ventilator techniques (high-frequency oscillatory ventilation, high-frequency percussive ventilation, airway pressure release ventilation) and adjunctive measures (lung recruitment maneuvers, prone positioning, inhaled nitric oxide, surfactants, extra-corporeal oxygenation devices) have been demonstrated to improve oxygenation in patients with severe hypoxemia, but these improvements in gas exchange have not yet translated to significantly improved survival. A recent large, randomized trial by the ARDS Network found no significant difference in mortality when patients were treated with a conservative versus a liberal fluid strategy, however only 8% of enrolled patients had traumatic ARDS. Similarly, corticosteroids for late phase ARDS did not improve mortality.Current recommendations include early use of lower tidal volumes (≤6 mL/kg PBW) and more widespread use of the ARDSNet ventilator algorithm. Patients who continue to have severe hypoxemia may be considered for high- frequency oscillatory ventilation (HFOV) or airway pressure release ventilation (APRV). Additionally, prone positioning may be utilized if not contraindicated. Adequately powered, randomized, controlled trials are needed to determine whether alternative approaches improve survival (and not just transient improvements in gas exchange).